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George Bevan

Deciphering the old world with new world technologies

Most people like to take a camera on holiday so they can snap photos of their favourite people and places. George Bevan is no different – except the pictures he takes aren’t going to be posted on Facebook or shared with Aunt Martha at Christmas.

Bevan, a professor of Classics at Queen’s, uses digital photography and sophisticated computer software to produce incredibly detailed three-dimensional images of everything from 19th-century shipwrecks to ancient carved inscriptions on rocks. The techniques he and his graduate-student colleagues are field testing promise to equip archaeologists and historians with a powerful new tool for studying and dating artifacts – and, in turn, to shed light on hitherto unsolvable historical mysteries.

“This will transform archeology.”

The technique, called photogrammetry, is a close cousin of stereoscopy, one of the earliest forms of 3D photography. You may have seen vintage stereoscopes in antique shops: they’re typically wooden sticks about a foot long, with a pair of magnifying eyepieces at one end and a slot for nearly-identical side-by-side photographs at the other end. When you slide photographs into the slot and view them through the eyepieces, the picture you see appears to be three-dimensional. This happens because the images, while they appear to be exactly the same, were in fact photographed from slightly different positions – which is how your eyes see things. Thus, when you view the pictures through the lenses, your brain is tricked into perceiving not only height and width in the images, but also depth.

Petroglyph and accompanying inscription that has been previously
erased.

Photogrammetry – determining the geometric properties of objects using photographic images – is stereoscopy on steroids. It allows a series of digital images of an object to be digitally converted into an incredibly lifelike model of the object that can be viewed and analyzed on a computer screen, or made into a video showing the object from multiple perspectives. It’s just as if you were examining the object in your hand, turning it this way and that, holding it at arm’s length or up close to your eye, or even using a microscope. It’s that realistic.

The photogrammetry software Bevan uses – Queen’s is one of only three Canadian universities licensed to use ADAMTech 3DM Analyst – was originally designed for the mining industry to allow mining engineers to map terrain (such as in an open-pit mine), identify geological hazards and find new deposits. Bevan, who is cross-appointed to the Department of Geology, first realized the potential of the technology after seeing it used to model the destroyed wellhead at the bottom of the Gulf of Mexico after the Deepwater Horizon oil rig explosion and oil spill in 2010. Bevan quickly realized that the same software could be adapted to other uses, such as the analysis of cultural heritage.

Last summer, for instance, he and his graduate student Michael Fergusson along with undergraduate Marla MacKinnon were in southern Jordan, snapping pictures of petroglyphs (rock carvings) on scores of boulders scattered on the scorching desert floor of a remote valley called Wadi Hafir.

The inscriptions, carved approximately 2000 years ago by Thamudic tribesmen, depict hunting scenes, animals, even sexual acts. Many carvers signed their names to their work, which – in combination with GPS co-ordinates of the boulders’ locations that Bevan’s collaborator Glenn Corbett collected for his PhD at the University of Chicago – allows archaeologists to deduce the family relationships and migration patterns that once existed in the area. As well, because it’s possible to zoom in on the carvings and measure the depth of the etching, the researchers can also determine whether an original carving was altered – and if so, what it looked like before the changes.

3D visualization of erased inscription using Screen
SpaceAmbient Occlusion (SSAO) filter in
CloudCompare, an open source point cloud analysis
package.

“If we have accurate depth information, we can, within limits, reconstruct the original,” says Bevan.

Since the 3-D images are so detailed – up to one-tenth of a pixel accuracy – it’s even possible to identify the individual carvers by the characteristic pattern of “peck marks” they left in their work. Another photographic tool Bevan uses is “gigapan,” a photographic technique pioneered by NASA scientists to capture extraordinarily high-resolution panoramic images of entire landscapes on the moon or on Mars. “Taking shots of the surrounding terrain helps contextualize the rock art,“ explains Bevan. “You can get a better sense of the physical environment the artists worked in and how it may have influenced them.”

Bevan’s other photogrammetry research has included analyzing the historic native rock carvings at Petroglyphs Provincial Park near Peterborough, Ontario with student Marla MacKinnon; computer modelling of the HMS Investigator, a British vessel which became trapped in the ice while searching for the lost explorer Sir John Franklin in the 1850s and whose sunken remains were discovered by Parks Canada scientists in 2010; and an analysis of the remains of the St. Lawrence, a Great Lakes warship built in Kingston during the War of 1812 whose remains lie on the bottom of Lake Ontario not far from the Queen’s campus.

“Photogrammetry is very old, but because of the evolution of computer technology we can now use consumer cameras to easily capture high-quality 3D images in remote locations,” says Bevan. “This will transform archeology.”